Speedometer temperature compensation



00L 11, 1955 R. H. MlTcHl-:L ETAL 2,720,503

SPEEDOMETER TEMPERATURE COMPENSATION Filed DBC. 28, 1951 60 Mp. h'.

GO 50 MM' INVENToRs fw //fm/ 21g 537. 4 BY @gg/vomi .5e/5gg nited StatesPatent O 'i SPEEDMETER TEMPERATURE COMPENSATN Ralph H. Mitchel andRaymond E. Schwyn, Flint, Mich., assignors to General MntorsCorporation, Detroit, Mich., a ccrporation o' Delaware AppiicationDecember' 23, 1951, Serial No. ZSS 8 Claims. (Ci. S10- 97) Thisinvention relates to magnetic measuring instruments and particularly tomeans for making the indications of instruments such as magneticspeedometers almost completely independent of variations in temperatureover an unusually Wide range of temperatures.

A speedometer of this type generally comprises a stationary field platewithin which is positioned a magnet adapted to be driven, directly orindirectly, from the shaft whose rotational speed is to be measured, anda drag element positioned in the magnetic field between the magnet andthe ield plate and adapted to be displaced from its position of rest adistance proportional to the speed of rotation of the shaft.

Such an instrument provides quite accurate speed indications whenoperated at the temperature at which it is calibrated, but if it isoperated at temperatures appreciably above or below this temperature,the speed indications will be considerably in error. This error iscaused by the fact that, while the strength of the magnetic fieldbetween the poles of the magnet and the iield plate remainssubstantially constant within the range of temperatures to beconsidered, the electrical resistance of the material of which the dragelement is made increases very considerably with increases intemperature and decreases proportionally with decreases in temperature.As is well known, the strength of the eddy currents induced in the dragelement by the moving lines of force between the magnet and the eldplate varies inversely with these variations in resistance andtemperature. Consequently, inasmuch as the detlection of the dragelement from its position of rest depends on the strength of the eddycurrents iiowing therein (the strength of the magnetic eld remainingconstant), the speed indication given thereby will be high attemperatures below, and low at temperatures above, that at which theinstrument is calibrated.

It is obvious that the indications of an instrument of the typedescribed will be unaffected by temperature changes if neither theelectrical resistance of the drag element nor the strength of themagnetic field passing through the drag element varies with changes intemperature. Since, as has been stated, the strength of the magnetic eldpassing through the drag element is practically constant throughout thetemperature range to be considered, this condition can be fulfilled bymaking the drag element of a material or combination of materials havinga temperature coeiicient of electrical resistance approaching zero. Suchmaterials exist but their electrical resistance is so high as to maketheir use in an instrument of this type impractical.

Accordingly, it has become a common expedient to make the drag elementof a material having a low electrical resistance with the accompanyingrelatively high temperature coeicient of electrical resistance. Theindications of such an instrument will be unaffected by temperaturechanges if the strength of the magnetic field passing through the dragelement thereof is caused to vary in such a manner as to compensate forthe changes in resistance of the drag element. This, of course, meansthat the strength of the magnetic field passing through the drag elementmust vary directly with the resistance of the drag element. Severalmeans of accomplishing this end have been proposed.

lf a piece of magnetic material having a negative 24,720,603 PatentedOct. 11, 1955 temperature coefficient of magnetic permeablity ispositioned so as to shunt a portion of the magnetic field of the magnetaway from the drag element, an increase in temperature Will cause lessof the flux from the magnet to ow into the shunt and more to flowthrough the drag element. Similarly, as the temperature decreases, moreof the magnetic flux will flow into the shunt and less through the dragelement. The use of such a shunt will, therefore, tend to compensate theinstrument for temperature changes.

Several magnetic materials having appreciable negative temperaturecoeicients of permeability are known, among which are certain alloys ofnickel and iron and certain alloys of nickel and copper. Heretoforeneither of these types of alloys, however, has proved to be entirelysatisfactory for all applications because of a lack of uniformity intheir corrective influence when the instruments are subjected to a verywide range of temperatures.

Operating temperatures for automotive speedometers normally areconsidered to range from 0 F. to 100 F., with a total error in thereadings of 4 miles per hour at a speed of 60 miles per hour beingpermissible. To meet this requirement, it has heretofore generally beensatisfactory to use a single temperature compensator of the above typein combination with a common type of steel magnet containing up to 3%cobalt or 6% chromium and a practically pure aluminum speed cup.However, many types of modern motor vehicles, particularly those whichare used for military purposes, are required to be equipped to operateunder extreme temperature conditions, such as those encountered inarctic and tropical climates. Accordingly, these requirementsnecessitate the use of speedometers which are compensated to registerspeed with a maximum error of 5% in a temperature range of minus F. toplus 160 F., for example. When an instrument of the type described aboveis subjected to these temperature conditions, its accuracy becomestotally inadequate, the temperature error in such cases commonly beingas great as 30 miles per hour over this wide temperature range.

Accordingly, it is a principal object of this invention to provide amagnetic measuring instrument which is highly accurate over an unusuallywide range of temperatures. More specifically, it is an object of thisinvention to provide a low-temperature compensating alloy for use in amagnetic measuring instrument to provide accurate instrument readings atextremely low temperatures.

A further object of this invention is to provide, in a magneticmeasuring instrument, a magnetic shunt in the form of a doublecompensator which is positioned between the poles of a magnet and whichpossesses such temperature-permeability characteristics as to counteractthe effects of variations in the electrical resistance of the dragelement on the indications of the instrument when subiected totemperatures ranging from minus 70 r. to F. Hence, this invention alsoencompasses the combination of a temperature compensating unit and ahigh ilux magnet which permit the use of a drag element having anunusually small temperature coefficient of electrical resistance withthe resultant advantages hereinbefore explained.

These and other objects are attained in accordance with our invention bythe provision of a shunt assembly consisting of a double temperaturecompensator. In this assembly one compensator plate is designed tocompensate for the high-temperature errors, while the other compensatorplate is formed from an alloy containing 2.5% to 6% manganese, 29% to31% nickel and the balance substantially all iron and is especiallyadapted to compensate for errors due to extremely low temperao os tures.These two plates preferably abut one another and act together to providea resultant compensation effect which renders the readings accurate atall temperatures.

Although two temperature compensating elements have previously beenjointly employed, this has been done only to produce a generallystraight temperatureperrneability curve through a relatively narrowtemperature range. This limited temperature compensation has beenaccomplished by using component elements one of which has atemperature-permeability curve which is concave upward and' the other ofwhich produces a concave downward curve through the same temperaturerange. The present invention, however, provides such an approximatelystraight li'ne function through a much wider range of temperatures bycombining compensators which supplement each other more efiiciently in adifferent manner. A high temperature range alloy is employed to producea temperature-permeability curve which is in itself unusually accurateat the higher temperatures, particularly those temperatures fromapproximately 50 F. to 160' F., while a second and novel alloy is usedto compensate for inaccuracies of the former at lower temperatures, suchas those ranging from approximately minus 70 F. to plus 50 F. Thislow-temperature range alloy provides this compensatory effect becauseits permeability rises sharply with decreases in temperatures withinthis lower temperature range. The high temperature range compensatorpreferably used is a nickel-iron type of alloy, such as that disclosedin Patent No. 1,988,568 which issued January 22, 1935, to Randolph etal.

To provide for optimum efficiency, we have found it desirable to employa magnet of high flux material, such as a 35% cobalt steel alloy, incombination with our double compensator unit. The use of such a strongermagnet permits the drag element to be formed of an aluminum-magnesiumalloy having a reduced eddy current drag and an exceptionally lowtemperature coeicient of electrical resistance. The change inresistivity in relation to temperature in this alloy is approximatelyonly one-half as large as that in the case of the approximately purealuminum speed cups conventionally used.

Other objects and advantages of our invention will more fully appearfrom the following description of the preferred embodiment shown in thedrawing, in which:

Figure 1 is a a fragmentary top plan view, with parts broken away and insection, of a speedometer embodying the invention;

Figure 2 is a fragmentary front sectional view along the line 2 2 ofFigure 1;

Figure 3 is a graph showing the temperature-permeability curves of thehighand low-temperature range compensators, and the composite curve ofthe temperature compensator unit resulting therefrom, over a wide rangeof temperatures, and

Figure 4 is a graph showing curves in which actual speeds are comparedwith speedometer readings at various temperatures.

Referring more particularly to the drawing, in Figure 1 is shown aspeedometer having a main supporting frame provided with an aperturedshank portion 12. Iournaled in this shank is a rotor shaft 14 having adriving worm 16 which meshes with another worm 18 on a transverselyextending shaft 2f?. This second worm shaft 26 is also rotatablyjournaled in frame 10 and is adapted to drive an odometer which, per se,forms no part of the invention and which therefore is not shown.

Axially adjacent the worm 16, the iirst worm shaft 14 and the shank 12of the frame 10 are provided with annular shoulders or flanges 22 and24, respectively, between which a thrust washer 26 is located. In thismanner, the shoulder 24 on the frame and the washer form an end bearingfor the shaft 14. The shank 12 of the frame is also shown as having arecess 28 containing a suitable wick 30 which is held in position by ametallic plug 32. The purpose of the wick is to carry a lubricant forlubricating the engaging surfaces of the shank 12 and the shaft 14.

The end of the first worm shaft 14 which is located within thespeedometer is provided with an axially extending recess 34 in which ispositioned a thrust bearing 36 secured in position by a jewel cup orhole jewel 33, which functions as a side bearing. This hole jewel ispreferably secured within the first worm shaft by staking the shaftagainstA it as indicated at 40. A spindle d2 has one end journaled inthe hole jewel Se and abutting the thrust bearing 36. The other end ofspindle 42 is similarly journaled inanother hole jewel and is providedwith the usual pointer to aid in reading the instrument, these parts notbeing shown inasmuch as they form no part of the invention.

A generally U-shaped magnet 44 having upstanding leg portions 46 and 48is secured by suitable means to the outer circumference of shaft 14radially adjacent the hole jewel 38. Positioned between these legportions or poles of the magnet and abutting the inner face thereof is atemperature compensating assembly comprising a pair of metallic plates59 and S2 of generally rectangular shape. These plates are attachedtogether by spot welding or other suitable means and are provided withcentral openings 54 and 56 through which the end of shaft 14 extends.The plate 50 immediately adjacent the magnet functions as a hightemperature range compensator, while the plate 52 is especially designedas a low-temperature range compensator. The compositions and magneticpermeability characteristics of the alloys of which these plates areformed will be hereinafter more fully described in the discussion of thetemperature compensating effects of this assembly over a wide range oftemperatures.

The 'end of shaft 14 is crimped over the inner edges of the hightemperature compensator plate 50, as shown at 5S, to attach thetemperature compensating plates to the magnet and to secure these partsto the shaft. Plates 59 and 52 are further prevented from rotatingrelative to the magnet by being provided with fmgers 6i? and 62,respectively, which are bent to frictionally engage the edges of themagnet.

A speed cup 64, which functions as a drag element, is coaxial with andpartially encases the magnet and temperature compensator assembly. Theside walls of the speed cup are shown as being cylindrical while thecentral portion of its end wall is provided with an opening 66 throughwhich the spindle 42 extends, the speed cup being rigidly secured to thespindle by soldering, as Shown at 68, or other suitable means.Concentric with and jacketing the speed cup is an annular field plate7), which is rigidly aixed to the frame 10 by screws or otherappropriate means, not shown. The speed cup, which is pivotally mountedso that its arcuate walls lie between the ends of the magnet and thearms of the armature, cuts the magnetic lines of force, and its rotationis affected by the magnetic drive in the usual manner.

A hairspring 72 has one end secured to the spindle 42 and its other endengaging the inwardly extending legs 74 and 76 of a hairspring tensionregulator 78, the hairspring being further coiled by the eddy currentsupon rotation of the magnet. The regulator 78, which is provided with anopening through which the spindle extends, in turn is attached to theadjacent end face of the stationary field plate 70 and is rotatablyadjustable thereon for regulating the tension of the hairspring.

In accordance with the invention, the low-temperature range compensator52 employed is an alloy comprising approximately 2.5% to 6% manganese,29% to 31% nickel, and the balance substantially all iron. Silicon andchromium may also be included in this alloy in amounts not in excess of2% and 2.8%, respectively,v but best results are obtained when thesilicon content is not greater than approximately 0.5%. Accordingly,optimum properties are present in a low-temperature range compensatoralloy containing 30% to 30.5% nickel, 3% to 4% manganese, 0.1% to 0.5%silicon and the balance substantially all iron.

ln this low-temperature range alloy the nickel content is veryimportant. Increasing the proportion of nickel raises the temperatureabove which the permeability of the alloy remains practically constantwith increases in temperature, this point commonly being known as theCurie point of the alloy. Moreover, raising the nickel content increasesthe amount of the alloy in the gamma phase within the aforementionednickel range and lowers its phase-change temperature, as well asincreasing the permeability of the alloy and the slope of itstemperaturepermeability curve.

inasmuch as small variations in the nickel content in this alloytherefore result in great differences in its temperature-responsivecharacteristics, it is important that the percentages be kept within thespecified limits. If the nickel content is increased above approximately31%, the Curie point of the alloy is raised to too high a temperature,and the temperature-permeability curve is too steep for practicalpurposes. To insure necessary permeability, on the other hand, thenickel content should not be lower 'than approximately 29%. If theamount of nickel is decreased below this percentage, the Curie point islowered and the phase-change temperature is raised to too great anextent, resulting in poor low-temperature stability. Below a nickelcontent somewhat less than 29% the alloy becomes very ineicient, andwith percentages not much below the minimum limit specified, the alloyhas magnetic transmission points within the operating range (minus 70 F.to plus 160 E).

The addition of manganese also affects the Curie point of thislow-temperature range alloy, a Curie point between 50 F. and 70 F. beingdesirable in the present instance. The Curie point is shifted toward thelower temperatures with increased amounts of manganese, the optimumshape of the temperature-permeability curve of this low-temperaturerange being obtained when the manganese content is maintained between 3%and 4%, although satisfactory results may be had with a manganesecontent of 2.5% to 6%. The temperature-permeability curve of the alloythus possesses a greater slope at the lower temperatures and contributesto provide a magnetic measuring instrument having greatly increasedaccuracy at these temperatures, the permeability of the alloy remainingpractically constant with changes in temperature at temperatures aboveapproximately 70 F. Moreover, the manganese improves the workingproperties of the alloy and aids in stabilizing it by preventing apermanent change in permeability upon exposure of the alloy to very lowtemperatures.

The percentage of silicon does not appreciably affect the permeabilityof the alloy nor the `slope of the temperattire-permeability curve ifmaintained below approximately 2%. However, the presence of this elementin quantities as low as 0.05%, the approximate minimum amount in whichit is normally present in commercial iron, aids in providing the alloywith low-temperature stability; and excellent results are obtained whenthe silicon content is between 0.1% and 0.5%. Other incidentalimpurities, such as phosphorus, carbon and sulphur may be introducedwith the iron in the usual small amounts, and their presence appears tohave little or no eifect upon the permeability of the alloy.

The alloy which is preferably used as the high-temperature rangecompensator 50 is a type containing from 29.75% to 30.5% nickel, carbonnot in excess of 0.25%, manganese not in excess of 1.0% and the balancesubstantially all iron. This latter type of alloy is disclosed in PatentNo. 1,988,568 to Randolph et al.

The particular alloys which should be used as a shunt with any giveninstrument will, of course', depend upon the temperature-resistancecharacteristics of the material of which the drag element is made, andthe amount of the alloy to be used will depend upon the strength of themagnet and the position of the shunt relative to the poles of themagnet. To provide for optimum eiciency in the use of our speedometer,therefore, we have found it desirable to employ a high flux magnetcontaining approximately 35% cobalt or equivalent high ilux material.Accordingly, we prefer to use a magnet formed from an alloy comprising33% to 35% cobalt, 4% to 5% tungsten, 1.5% to 2% chromium, 0.3% to 0.5%manganese, 0.7% to 0.9% carbon and the balance substantially all iron.

Such a magnet permits the use of a hairspring which may be as much asthree or four times as strong as those which heretofore have been usedin similar instruments. With such a substantially stronger hairspringthe effects of jewel friction become negligible, and excessive sway ofthe indicating pointer is eliminated. Furthermore, the use of this highux magnet also permits the speed cup to be formed of analuminum-magnesium alloy having a reduced eddy current drag and whosechange in resistivity in relation to temperature is approximately onlyone-half as large as in the case of a pure aluminum speed cup. When suchan alloy is used instead of pure aluminum to form the speed cup, thisstronger magnet compensates for the reduced eddy current drag from thealuminum alloy.

The speed cup which is used in combination with the above-describedtemperature compensating assembly and high flux magnet, therefore, ispreferably an alloy containing approximately 2% to 3% magnesium. Thus wehave found an alloy having the following composition to be particularlyeffective as a drag element: 2.2% to 2.8% magnesium, 0.15% to 0.35%chromium, iron plus silicon not in excess of 0.45%, manganese not inexcess of 0.10%, Zinc not in excess of 0.10%, copper not in excess of0.10%, and the balance substantially all aluminum. The use of this typeof speed cup alloy with the double compensator and magnet provides aspeedometer whose readings are particularly accurate over allpracticable temperature ranges.

The construction described above is highly etlicient due to the upturnedends of the magnet and the parallel walls of the speed cup. Furthermore,shaping the eld plate to enclose the speed cup and magnet to therebyshield all the available magnetic flux for efficient influence on thespeed cup permits substantially the entire magnetic iield to beutilized. Since the full strength of the magnet is being used within thespeed cup, a more definite control is provided than with otherarrangements, both the active field and the shunt being shielded. Theelectrical resistance characteristics of the speed cup metal totemperature changes may be accurately measured and the dimensions of thecompensator plates determined so as to insure very accurate readings atall temperatures.

For best results the temperature compensator plates are arranged in themanner hereinbefore described and shown, with the high-temperature rangeplate 50 being positioned between the magnet and the low-temperaturerange plate 52. Reversing the positions of these plates may result inerrors in the readings as high as 25% or 30%.

We have thus provided a temperature compensator assembly which isattached to the rotating magnet and positioned within the magneticfield. This assembly constitutes a shunt which permits the reducedelectrical resistance of the speed cup tending to cause the readings tobe too high at low temperatures to be compensated by the increasedpermeability of the compensator plates. At temperatures above those forwhich the instrument is calibrated, on the other hand, the reverse istrue, the reduced permeability of the double compensator permitting moreof the ilux to pass through the speed cup to counteract the increasedresistance of the speed cup. Hence the temperature compensating assemblydirectly controls the proportion of the. magnetic ux whichy passesthrough the speed cup to lthereby provide maximum accuracy of speedindication over an exceptionally wide temperature range.

The eiciency of the above-described double compensator' assembly can beseen from the curves shown in Figure 3. In this graph, the abscissas ofthe curves are temperaturesv ranging from minus 70 F. to plus 160 F.while. the ordinates represent the magnetic permeability ot thecompensating plates While. subjected to a magnetic eld of constant,strength, the particular curves shown resulting whenv the iieldintensity was, 46 gilberts per cm. From this graphit can be seen thatthe high-temperature range alloy employed produces atemperature-permeability curve which is itself unusually accurate at thehigher temperatures,r particularly those temperatures from approximately50 F. to 160 F., while the low-temperature range alloy used has atemperature-permeability curve whose slope is considerably greater atthe lower temperatures, especially those between minus 70 F. andapproximately plus 50 F., than at the higher temperatures. In thismanner the low-temperature range alloy compensates for inaccuracies ofthe high-temperature range alloy which result from thetemperature-penneability curve of the latter having too small a slope atthese lower temperatures. Hence, the composite of these two curves is asum or resultant which is a generally straight line through the widetemperature range from minus 70 F. all the way to plus 160 F.

As can be seen from Figure 4, wherein speedometer readings in miles perhour are plotted against temperature, the actual speeds indicated by thetwo curves vary insigniicantly from the speedometer readings. This istrue both at lower speeds, as indicated by the thirty miles per hourcurve, and at higher speeds, as shown by the sixty miles per hour curve.It will be noted, in fact, that over the temperature range from minus 65F. to plus 160 F., the 60 miles per hour curve indicates that there wasapproximately only a two miles per hour maximum variation between thespeedometer reading and the actual speed of the vehicle being tested.The 30 miles per hour curve shows that the inventive speedometer is evenmore accurate at lower speeds over this wide temperature range, themaximum variation in the speedometer readings being approximately onlyone mile per hour in this latter instance. Thus it will be seen thatthis invention provides a magnetic measuring instrument in which errorsdue to temperature are only slightly over 3% when the instrument issubjected to all temperatures which might possibly be encountered.

It is to be understood that, while our invention has been described bymeans of certain specific examples, the scope of our invention is not tobe limited thereby except as dened in the appended claims.

We claim:

1. A temperature-responsive compensator for magnetic measuringinstruments formed from an alloy containing 2.5% to 6% manganese, 29% to31% nickel, and the balance substantially all iron.

2. A temperature-responsive compensator for magnetic measuringinstruments formed from an alloy comprising 2.5 to 6% manganese, 29% to31% nickel, silicon not in excess of 2%, and the balance substantiallyall iron.

3. In a magnetic measuring instrument, a temperatureresponsivecompensator for correcting errors in readings due to low temperatures,said compensator being formed from an alloy comprising 3% to 4%manganese, 30% to 30.5% nickel, 0.1% to 0.5% silicon, and the balancesubstantially all iron plus incidental impurities.

4. In a measuring instrument, the combination of a rotatable magnet anda magnetic shunt positioned in the magnetic iield of said magnet, saidshunt comprising an alloy for compensating for high-temperature rangeerrors, and a dissimilar alloy for compensating for low-tem- S peraturevrange errors and containing 2.5 to 6% manganese, 29% to. 31% nickel andthe balance substantially all iron.

5. In a magnetic measuring instrument, the combination of a main frame,a magnet rotatably supported by said frame, and a magnetic shuntpositioned in the magnetic field of saidY alloy, said shunt comprisingtwo bodies of dissimilar alloys, one of said bodies compensating forhigh-temperature range, errors, the other of said bodies compensatingfor low-temperature range errors and cornprising 2.5% to 6% manganese,29% to 31% nickel, silicon not in excess of 2,% chromium not in excessof 2.8%, and the balance substantially all iron.

6. Inl a magnetic measuring instrument adapted for use over a widetemperature range, the combination of a main frame, a magnet rotatablysupported by said frame, a temperature compensating assembly positionedbetween the poles of said magnet and rotatable therewith, saidcompensating assembly comprising a high-temperature range compensatorplate containing between 29.75% and 30.5 nickel and the balancesubstantially all iron, said high-temperature range compensator platebeing positioned against the lower surface of said magnet, and alow-temperature range compensator plate comprising 2.5% to 6% manganese,29% to 31% nickel, and the balance substantially all iron, saidlow-temperature range compensator plate being positioned against theside of the high-temperature range compensator plate opposite saidmagnet.

7. In a magnetic measuring instrument for use over a wide temperature.range, the combination of a main supporting frame, a stationary eldplate affixed to said frame, a magnet rotatably positioned within saideld plate, a drag element interjacent said magnet and said ield plateand mounted for differential rotation with said magnet, and a magneticshunt comprising two bodies ot dissimilar alloys4 secured to the bottomof said magnet and located between the poles thereof, one of said alloysconstituting a low-temperature range compensator and containing 3% to 4%manganese., 30% to 30.5% nickel, 0.05% to 2% silicon, and the balancesubstantially all iron plus incidental impurities, the other of saidalloys constituting a high-temperature range compensator and being,positioned interjacent said magnet and said lowtemperature rangecompensator.

8. In a magnetic measuring instrument to be used over a wide temperaturerange, the combination of a main supporting frame, an aluminum base dragelement containing 2% to 3% magnesium rotatably supported by said frame,a high flux magnet positioned generally within and coaxial with saiddrag element for differential rotation therewith, and a magnetic iiuxcompensating assembly positioned between the poles of said magnet andsecured thereto to rotate therewith, said compensating assemblycomprising a high-temperature range compensator plate and alow-temperature range compensator plate, said low-temperature rangecompensator plate being formed from an alloy comprising 2.5% to 6%manganese, 29% to 31% nickel, silicon not in excess of 2%, and thebalance substantially all iron.

References Cited in the le of this patent UNITED STATES PATENTS1,697,580 Wallis Ian. 1, 1929 1,968,971 Sullivan Aug. 7, 1934 1,988,568Randolph Ian. 22, 1935 2,232,789 Kollsman Feb. 25, 1941 2,648,019Rodanet Aug. 4, 1953 OTHER REFERENCES Alloys of Iron and Nickel, vol.lI, page 406. Edited by Marsh. Published in 1938 by the McGraw-Hill BookCo., New York.

Metals Handbook, 1948 edition, pages 600 and 601. Published by Amer.Soc. for Metals.

1. A TEMPERATURE-RESPONSIVE COMPENSATOR FOR MAGNETIC MEASURINGINSTRUMENTS FORMED FROM AN ALLOY CONTAINING 2.5% TO 6% MANGANESE, 29% TO31% NICKEL, AND THE BALANCE SUBSTANTIALLY ALL IRON.